The following references are believed to represent the state of the art:
U.S. Pat. No. 7,526,808 to Lynn, et al.;
U.S. Pat. No. 7,624,282 to Hollar;
U.S. Pat. No. 7,721,333 to Home;
US Published Patent Application 2007/0169191 of Greene, et al.;
US Published Patent Application 2008/0208560 of Johnson, et al.;
US Published Patent Application 2008/0216051 of Johnson, et al.; and
US Published Patent Application 2011/0060915 of Tal.